We have created a filter that requires moderation intervention for all messages with Korean characters from new users. The impact should be minimal, but posts from new users will only appear after a few minutes delay.

In this case, '야' would say that 'Hey'.
More, it is the one of name for calling someone who would be same age or younger than one person.
But we shouldn't use it any case because it is informal.
And sometimes this word have a meaning that someone pay no mind to one another.
So we should use it between 2 or more persons who are very close friends and known each other for many times.
And it could be often used to start to say something adding few words.
For example,
'Hey, cheol-soo.' : 야, 철수야.
'Hey, as you know' : 야, 있잖아.. or 야, 너도 알다시피.. or 야, 근데..

What 경상남도로 오이소 is partly wrong. 형 doesn't become 동생 nor 동생 becomes 형, etc.
You aren't changing social standing as Superhero says.
You don't make 형 to use honorifics to 동생. Everyone uses 반말 to each other, hence 야자(반말)타임.
Because 형 would use 반말 to 동생 anyway, only 동생 has gain but not 형.
Also the game is usually played while drunk things can go out of control.
If you get to play, don't forget about the aftermath as some people may hold grudge after the game...